The present invention relates to a color filter comprising green pixel portions containing a halogenated metal phthalocyanine pigment.
In a liquid crystal display device, a color filter comprises a transparent substrate on which red pixel portions, green pixel portions, and blue pixel portions are formed, and halogenated copper phthalocyanine dyes or halogenated copper phthalocyanine pigments are generally used for the green pixel portions.
As a green colorant for the green pixel portions of the color filter, there is used a dye or pigment having a structure of a halogenated metal phthalocyanine wherein 8 or more halogen atoms are bonded to benzene rings in one phthalocyanine molecule. However, for dyes or pigments used in the field of color filters, which are different from those for general purposes such as lithographic inks, paints, and coloring of molded articles, there is required not only coloring characteristics, but also the following higher characteristics (1) and (2):
(1) high selectivity of the wavelength of light which penetrates, and
(2) very high transmittance of light having a specific wavelength.
Japanese Unexamined Patent Application, First Publication No. Sho 63-286801 discloses a technology which uses, as such a green dye colorant, a halogenated metal phthalocyanine sulfonate dye such as octachloro copper phthalocyanine sulfonate dye, octachloro nickel phthalocyanine sulfonate dye, or octachloro cobalt phthalocyanine sulfonate dye in combination with a yellow organic dye.
Also, Japanese Unexamined Patent Application, First Publication No. Hei 11-302283 discloses a technology which uses a phenylated metal phthalocyanine sulfonate dye such as octaphenyl copper phthalocyanine sulfonate dye, octaphenyl zinc phthalocyanine sulfonate dye, or octaphenyl aluminum phthalocyanine sulfonate dye in combination with a yellow organic dye.
Furthermore, Japanese Unexamined Patent Application, First Publication No. Hei 9-291240 discloses a technology which uses a green copper phthalocyanine dye having a sulfonic acid group and a monoazo dye residue, and a green zinc phthalocyanine dye having a sulfonic acid group and a monoazo dye residue.
However, these dyes have drawbacks in that they are inferior in the durability of various characteristics such as light resistance.
As a green pigment with fewer of the drawbacks described above, there is commonly used a halogenated copper phthalocyanine pigment wherein 8 or more of hydrogen atoms among 16 hydrogen atoms on 4 benzene rings in one phthalocyanine molecule are substituted with halogen atoms such as bromine and chlorine atoms. This halogenated copper phthalocyanine pigment is a mixture of halogenated copper phthalocyanine pigments wherein hydrogen atoms are substituted with bromine atoms and/or chlorine atoms in different ratios.
For the green pixel portions of the color filter, a brighter green pigment having a stronger yellowish tinge is required. It has conventionally been deemed to be preferable that the number of halogen atoms bonded to benzene rings in one halogenated copper phthalocyanine molecule be increased in order to develop a bright green color having a strong yellowish tinge. Also, it has been known that as the number of bromine atoms among halogen atoms bonded to one halogenated copper phthalocyanine molecule increases, a green color having a stronger yellowish tinge can be developed. For example, Japanese Unexamined Patent Application, First Publication No. Hei 9-68607 proposes a method of using, in green pixel portions of a color filter, a halogenated copper phthalocyanine pigment containing a high-bromine content halogenated copper phthalocyanine such as C.I. Pigment GREEN 36 wherein numerous hydrogen atoms among 16 hydrogen atoms on 4 benzene rings in one phthalocyanine molecule are substituted with bromine atoms.
Also Japanese Unexamined Patent Application, First Publication No. Hei 10-160928 proposes a method of adding a yellow pigment such as C.I. Pigment YELLOW 150 or C.I. Pigment YELLOW 185 to a green pigment such as C.I. Pigment GREEN 36, thereby imparting a stronger yellowish tinge, for the purpose of changing a color hue so as to increase the yellowishness of a green color.
However, as a backlighting light source of a liquid crystal display device, a three-band lamp having a main emission line of green light of about 545 nm is used, and the following problems arise when using the above-described conventional color filter in a liquid crystal display device using this light source.
Any color filter using the green dye described in the aforementioned Japanese Unexamined Patent Application, First Publication No. Sho 63-286801 has fundamental drawbacks such as poor light resistance and fading of color hue during use over long periods.
Also, green pixel portions of color filters produced by using C.I. Pigment GREEN 36 as the green pigment described in Japanese Unexamined Patent Application, First Publication No. Hei 9-68607 cannot achieve desired chromaticity and desired color hue, which are suitable for red pixel portions and blue pixel portions to be used in combination.
Furthermore, Japanese Unexamined Patent Application, First Publication No. Hei 10-160928 proposes to bring the chromaticity and color hue of pixel portions close to the desired chromaticity and desired color hue by adding a yellow pigment to C.I. Pigment GREEN 36. However, the amount of the yellow pigment to be added to the green pigment for the purpose of achieving this object is high, thus portions with neither desired chromaticity nor desired color hue in the pixel portions are sometimes formed for the following reason.
That is, the yellow and green pigments used in combination during the storage of a photocurable composition described hereinafter used to form pixel portions cause color separation.
Consequently, a color filter having such pixel portions has drawbacks in that the resulting liquid crystal display has insufficient brightness and a backlighting light source with a high intensity must be used to display satisfactory bright images, and that portions with neither desired chromaticity nor desired color hue is formed in the pixel portions.
An object to be achieved by the present invention is to provide a color filter which is more durable than a dye-type color filter and also has green pixel portions which can produce a bright green color having a stronger yellowish tinge when used in a liquid crystal display device using a three-band lamp having a main emission line of green light of about 545 nm as a light source, and thus enabling the liquid crystal display device to display bright images even when using a backlighting light source having a low intensity.
The present inventors have synthesized various halogenated metal phthalocyanine pigments having characteristics superior to those of a conventional halogenated copper phthalocyanine pigment used to form green pixel portions of a color filter and measured the respective transmission spectra, and then researched on the suitability as green pixel portions.
In the three-band lamp used in an actual liquid crystal display device, the emission wavelength is sometimes optimized in order to enable it to suit each color filter, and use of a three-band lamp in the evaluation of the present invention is a complicated operation. Therefore, in light of the fact that a main emission line of green light of the three-band lamp is about 545 nm, the evaluation was conducted by using a three-band fluorescent lamp F10 light source having a main emission line at 545 nm, which is a type of this three-band lamp, specified in Japanese Industrial Standard (JIS) Z8719, in place of the three-band lamp used in the actual liquid crystal display device. As a result, the present inventors have found that, when using, as a colorant for forming green pixel portions, a specific halogenated metal phthalocyanine pigment, which exhibits maximum transmittance at a wavelength within a range from 520 to 590 nm with respect to the transmission spectra, there can be provided a bright liquid crystal display device which exhibits a bright green color having a stronger yellowish tinge. Thus, the present invention has been completed.
The present invention provides a color filter comprising a transparent substance and red pixel portions, green pixel portions, and blue pixel portions formed on said transparent substrate, wherein said green pixel portions (1) contain a halogenated metal phthalocyanine pigment in which 8 to 16 halogen atoms are bonded to benzene rings in one phthalocyanine molecule, and (2) exhibit maximum transmittance at a wavelength within a range from 520 nm to 590 nm with respect to the transmission spectra of the entire range of visible light.